qid int64 1 4.65M | metadata listlengths 3 3 | prompt stringlengths 31 25.8k | chosen stringlengths 17 28.2k | rejected stringlengths 19 40.5k | domain stringclasses 28
values |
|---|---|---|---|---|---|
355,526 | [
"https://physics.stackexchange.com/questions/355526",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/166395/"
] | I was wondering how the Bohm interpretation of quantum mechanics would affect the Schrodinger's cat experiment. Would it imply that the cat would be in one state and never in superposition, so the cat would always be dead or alive whether or not the observer looks or not?
| In Bohmian mechanics, the state of the system is not just given by the wave function $\psi$: it is given by the pair $(\psi, Q)$ where $Q$ is the position in the configuration space. Here $Q$ collectively denotes the positions of all the particles the cat is made of, their spin, … you name it. So $\psi$ is still the su... | Since this came up again, here are my two cents:
<blockquote>
I was wondering how the Bohm interpretation of quantum mechanics would affect the Schrodinger's cat experiment.
</blockquote>
Bohmian mechanics give the same predictions as the usual non relativistic quantum mechanics, using a different model. AFAIK spec... | https://physics.stackexchange.com |
115,366 | [
"https://electronics.stackexchange.com/questions/115366",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/40929/"
] | Truth table :
<img src="https://i.stack.imgur.com/bfM77.png" alt="enter image description here">
Circuit :
<img src="https://i.stack.imgur.com/dVdLx.png" alt="enter image description here">
This circuit is created with K-map so it should have been simplified. Is it possible to reduce the number of logic gates by g... | In this instance I can see no way of reducing the number of logic gates. You can only "share" gates if the inputs are the same between instances of a gate, or they share a subset of the inputs that could be separated off into another gate.
The only optimization I can see at the moment is:
$$A_1 = D_2 + D_3$$
$$V = D... | The top line of the truth table should read:
<pre><code> D3 D2 D1 D0 A1 A0 V
|---|---|---|---|----|---|---|---|
0 0 0 0 0 0 0
</code></pre>
| https://electronics.stackexchange.com |
30,971 | [
"https://electronics.stackexchange.com/questions/30971",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/9510/"
] | I tried to simulate a circuit with mosfets in LTspice, but it's still hard to understand how they work
<img src="https://i.stack.imgur.com/Q4OMz.jpg" alt="enter image description here">
What I observed:
<hr>
For N-channel MOSFETs (as in the picture above)
a) Current flow through N-channel MOSFET transistor
<ol>
<... | I'll just answer the NMOS part of your question. The answers for PMOS are similar, so the explanation should carry over.
<blockquote>
a) Current flow through N-channel MOSFET transistor
<ol>
<li>Does not depend on V1's voltage</li>
<li>Depends on V2's voltage</li>
<li>Does not depend on the current charging the gate (f... | I think what you are seeing is a artifact of a corner case of the simulator. Ironically, you'd probably get about the same result with a real circuit, but for a different reason. That is because a real voltmeter has a finit resistance, so will load the drain even if it is otherwise not connected to anything.
When th... | https://electronics.stackexchange.com |
314,938 | [
"https://mathoverflow.net/questions/314938",
"https://mathoverflow.net",
"https://mathoverflow.net/users/120302/"
] | Let <span class="math-container">$S=\{1,2,\cdots,2n\}$</span>, and <span class="math-container">$S_i \subseteq S(i=1,2,\cdots,n+1)$</span> be <span class="math-container">$n+1$</span> subsets, each of which contains half of the <span class="math-container">$2n$</span> elements, namely <span class="math-container">$|S_i... | Here is an answer to the first point and shows how you can also do the third point.
Let <span class="math-container">$\displaystyle \bigcup_{i=1}^{n+1} S_i=\{b_{1},b_{2},\ldots, b_{m}\}$</span>.
We consider the following table with rows indexed by the sets <span class="math-container">$S_1,S_2,\ldots, S_{n+1}$</span> ... | <strong>An answer to your fourth question:</strong>
The Welch lower bound (applicable to arbitrary complex vectors, as opposed to the Sidelnikov lower bounds applicable only to vectors with entries in the complex roots of unity, which are somewhat tighter) states that for any
integer <span class="math-container">$f\ge... | https://mathoverflow.net |
371,620 | [
"https://softwareengineering.stackexchange.com/questions/371620",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/306793/"
] | Suppose I have a private project with 100 commits. I don't add a software license until the 101st commit. If I make the project open source, does that mean all first 100 commits are unbound by the software license in the 101st commit?
Should the project be rebased when a license is added?
| The licence applies when you publish the work. So if you publish after the commit then it covers all of the commits.
If you publish before you add the licence, then there is no licence for anyone to use your copywrited work until you publish a version under a licence of some kind.
The problem you are thinking of occu... | You are correct that the license is valid from the time it is applied. That means that the previous commits are defaulting to copyright which means no one has the right to use them for any purpose.
If it is important to you that others can use the old versions you could rebase.
| https://softwareengineering.stackexchange.com |
427,644 | [
"https://physics.stackexchange.com/questions/427644",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/148594/"
] | $W$ and $Z$ bosons should decay through <strong>weak</strong> interaction. But their half-life is around $\tau = 10^{-25} s$ which is a typical value for particles decaying through <strong>strong</strong> force (instead of a $10^{-12}-10^{-6} s$ for a weak interaction decaying particle).
Why this can be?
| Yes, it <em>is</em>
<blockquote>
correct to say that the W boson is decaying through weak interaction despite its very small lifetime.
</blockquote>
The weak interactions were dubbed such in the last century because, at low energies compared to the mass of the <em>W</em>, about 80GeV, the large mass of this partic... | Both are weak decay processes but the intermediate vector boson decay occurs at very much higher energies of 80-90 GeV compared to 1 GeV for beta decay.
| https://physics.stackexchange.com |
187,660 | [
"https://security.stackexchange.com/questions/187660",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/180147/"
] | At my workplace only the security team have access to see the rules on the server network firewalls.
Developers and system engineers don't have any visibility, so they just deploy applications to servers and find out what's broken rather than checking application requirements against the rules in advance.
Is this... | It is normal that the only people with access to view and review the network rules are the network engineers and the security team.
The development team should know what ports and protocols are required to use their applications and work with the networks team to ensure the appropriate rules are in place. If there are... | It is normal. The rules have to be documented, but no other teams should know them.
Developers and system engineers may request for rules to be added (or removed if no longer needed) and that's more than enough.
This is a very good security practice and should remain so.
| https://security.stackexchange.com |
358,743 | [
"https://softwareengineering.stackexchange.com/questions/358743",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/44681/"
] | A team simultaneously made several refactorings (to raise system genericity) to the same project with some overlaps (yes, unfortunately, more like "big bang"). Code is spanning representation, application, domain layers and has pretty high code coverage. There are N branches waiting to be merged into the master. Some r... | You merge in the order that makes the merges the easiest. There is no general heuristic for this because it's highly dependent upon the code changes in question. Most of the time, your "gut feel" is pretty close to optimal. Consider that you can test different merge orders locally before doing it officially for your... | Merge in order of completion. Otherwise people are hanging around waiting for stuff.
Lets say you have two simultaneously complete branches to merge
branch 1 is a small change, the Add function is now called Addition and take an extra parameter (so the ide cant automatically make the change)
branch 2 is a large cha... | https://softwareengineering.stackexchange.com |
280,667 | [
"https://softwareengineering.stackexchange.com/questions/280667",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/171139/"
] | I am to build a python function that takes a sorted list of numbers and outputs the first index the is equal to the element in its place.
It should run on O(log n) which I know how it should be running, operationally, but I can't manage to implement it. I guess I should check if the first element fulfills the require... | Forget my earlier answer. I actually implemented it now and it works. Not spoiling the whole thing but just answering your question, here's part of my code:
<pre><code>def Fun(I):
lo, hi = 0, len(I) # We'll search I[lo:hi], i.e., excluding index hi
while lo < hi:
check middle index
adjust... | Don't slice your list, pass start and end indices instead
<pre><code>def Fun(I):
def Inner(I, L, R):
for i in range(L,R):
if i==[i]:
return i
elif I[len(I)/2-1]>len(I)/2-1:
return Inner(I, L, L + (R/2))
else:
return Inne... | https://softwareengineering.stackexchange.com |
40,112 | [
"https://security.stackexchange.com/questions/40112",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/28570/"
] | I have created a public private key pair using the KeyPairGenerator class in Java. From this key pair I have generated the CSR request using the PKCS10 class which has been sent to a CA for verification. The question is how do I load this public private key pair into a keystore? I cant use KeyStore.SetKeyEntry as it re... | You seem to be mixing two security objectives: protection of the code against reverse engineering, and protection of the application against attacks. These objectives are often contradictory: protections against reverse engineering increase the complexity of the code and therefore make it more likely that the code is v... | In many programming languages, initialization of local variables is forced, or the engine will flatly refuse to read uninitialized data. Even in languages where you <em>can</em> read uninitialized variables and thus get a copy of what remained in RAM at that emplacement, you cannot count on it to be "random"; it will h... | https://security.stackexchange.com |
91,021 | [
"https://mathoverflow.net/questions/91021",
"https://mathoverflow.net",
"https://mathoverflow.net/users/11546/"
] | Suppose I have a spectrum $X$ and two homology theories $E$ and $F$. If I look at the Bousfield localizations, $L_E$, $L_F$, $L_{E\vee F}$ and $L_{E\wedge F}$, do I have a homotopy pullback square whose top row is $L_{E\vee F}(X)\to L_E(X)$, and whose lower row is $L_F(X)\to L_{E\wedge F}(X)$? If not, is it known what... | I think the best available statement is as follows. Suppose that $E$ and $F$ have the property that whenever $F\wedge X=0$ we also have $F\wedge L_EX=0$. (This holds if $L_E$ is smashing, for example when $E$ is the Johnson-Wilson spectrum $E(n)$.) Then there is a natural homotopy pullback square
$$ \begin{array}{cc... | I am not really a MathOverflow reader, but I just came across this discussion. I first saw the fracture square that Neil describes (in the classic case of interest as above) in a (handwritten) letter to me from Pete Bousfield dated January 22, 1987. It is in the midst of a paragraph that begins with " ... I'll make s... | https://mathoverflow.net |
28,098 | [
"https://dba.stackexchange.com/questions/28098",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/14995/"
] | I'm working on a ASP/MS SQL project that performs a lot of calculations based on dates and time. In one case, the system will lookup a value based on the nearest half hour increment throughout the day.
When designing the database should I create a lookup table with just the increments, for example: 00:00:00, 00:30:00... | You can create a time table which stores time in minutes. Then have a column as the foreign key to the record which has got half an hour difference to it. If you need to get half an hour before a time slot and half an hour after it, you will have 2 columns. One referring to the record which has got the half an hour pri... | Assuming you have some kind of transaction table containing events that occur at various times throughout the day, then the best thing is to start by recording these events with the full date and time to whatever precision you like in one table.
To group these events into time periods for reporting, you can create a r... | https://dba.stackexchange.com |
96,178 | [
"https://dba.stackexchange.com/questions/96178",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/61679/"
] | I have my VPS server in a remote location with ip address 172.16.11.2 (for example) having two instances of sql-server express running.
one instance is <strong>Microsoft SQL Server 2008 R2 (SP2)</strong> where I connect from my local PC using remote desktop with the following credentials:
<pre><code> servername : 17... | Ensure that the secondary instance (in this case SQL Express) has a TCP port set.
<ol>
<li>Under SQL Server Configuration Manager, go to SQL Server Network Configuration, then Protocols for [INSTANCENAME]. </li>
<li>Right click TCP/IP and under the IP Addresses tab make sure the field "TCP Port" has a value (for examp... | type in run command -> <code>mstsc</code>
then remote desktop connection window will be pop-up. That window will
ask your Computer and User Name
In "Computer Name" field there will be your "Remote Desktop IP address"
and "User Name" field type your local computer UserID, from which userid your did login in your loc... | https://dba.stackexchange.com |
226,403 | [
"https://mathoverflow.net/questions/226403",
"https://mathoverflow.net",
"https://mathoverflow.net/users/75786/"
] | On a (simply connected) domain $\Omega$ for a smooth vector field $F\colon \Omega \to \mathbb{R}^3$, when does $\nabla\times(\nabla\times F)=0$ imply $\nabla \times F=0$. I know that $n\cdot(\nabla\times F)=0$ on $\partial\Omega$ is sufficient, and also $t\cdot(\nabla\times F)=0$ is sufficient ($t$ the tangential). Is ... | Here are some basic thoughts. Let $G$ be a vector field which is of the form $\nabla \times F$, and also obeys $\nabla \times G = 0$.
Since $\nabla \times G = 0$, the vector field $G$ is locally of the form $\nabla h$ for some scalar valued function $h$. The condition that $G = \nabla \times F$ imples that $\nabla \cd... | For some scalar function g: $ rot\ F=grad\ g$. Necessary and sufficient!
| https://mathoverflow.net |
74,159 | [
"https://physics.stackexchange.com/questions/74159",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/28249/"
] | I'm not so technical and not very good with physics, but have some idea based on observation and I believe it is doable.
As everyone know also this subject was repeated many times in here,
Sending stuff to space is very expensive. But what if there is an easy way to do that only if we would think out side the box.
... | You are getting confused between work done by a <em>single force</em> and <em>total work done</em> on a body. When you substitute $F=mg$ in the above equation<sup><strong>[1]</strong></sup>, you are calculating the work done <em>by the gravitational force</em>, only the gravitational force and nothing else.
Substituti... | When you accelerate the object the applied force is greated than gravity. The formula is
$$ F = m ( g + \ddot{y} ) $$
where $\ddot{y}$ is the upwards acceleration. The work put in the system is equal to the work needed to lift the object (potential energy) plus the work needed to move the object (kinetic energy).
Th... | https://physics.stackexchange.com |
96,331 | [
"https://softwareengineering.stackexchange.com/questions/96331",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/30851/"
] | I am really confused with this. I believe that the more I am getting experience, the more I am becoming an expert at finding mistakes and fixing them quickly.
Now my boss got website from a programmer who does very very bad coding.
Now he sends the list of problems to fix.
Suppose it's the stylesheet problem, and the... | Such a good question because it is a problem we all face as freelancers. When I made the transition to being a freelancer, the hardest thing for me to develop was a time tracking discipline. For the first year or so, I just focused on project-oriented work, and really only bothered with timers when I was "in the zone" ... | You're paid by hour, and for your experience, right? Then what's the problem?
Somebody pays you to do something you actually can do according to your skills and accepting your per-hour rate. So just do it. Why would you compare yourself to some beginner who will spend doing the same thing ten times longer? If you beli... | https://softwareengineering.stackexchange.com |
132,199 | [
"https://physics.stackexchange.com/questions/132199",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/57641/"
] | Does the cross product of two vectors result in a vector perpendicular to both of the vectors <em>or</em> does the cross product of <strong>only two perpendicular</strong> vectors result in a vector perpendicular to both of the vectors?
| The cross product of two vectors, be there any angle between them, is perpendicular to the two vectors. It is, more precisely, perpendicular to the <em>plane</em> containing the two vectors. The direction is determined by the <em>right hand thumb rule/corkscrew rule</em>. The magnitude of the vector is given by $|{\bf ... | <blockquote>
Is the cross product of two vectors always perpendicular to both?
</blockquote>
No. The cross product is the zero vector if one or both of the vectors is the zero vector, or if the two vectors are parallel or anti-parallel to one another. The angle between the zero vector and some other vector is indete... | https://physics.stackexchange.com |
1,754,265 | [
"https://math.stackexchange.com/questions/1754265",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/316437/"
] | I am trying to understand a part of the proof of Theorem 9.2 of Rudin's book "Principles of Mathematical Analysis".
The theorem says: Let $r$ be a positive integer. If a vector space $X$ is spanned by a set of $r$ vectors, them $dim X \leq r$.
The proof is by contradiction. He supposes that there is a space X that is... | By dimensional analysis, we know the result has dimension $\text{length}^{-1}$. This immediately rules out choice $B$ and $C$. If this is an exam, I will probably
just write down the result as $A$, move on and revisit the problem when I have time.
When one need to really solve this, one can use choice $A$ as an ansatz... | we have
$$h_a=\frac{2A}{a}$$ etc and we get
$$\frac{1}{2A}(a\cos(\alpha)+b\cos(\beta)+c\cos(\beta))=\frac{2R}{abc}\left(\frac{a(b^2+c^2-a^2)}{2bc}+\frac{b(a^2+c^2-b^2)}{2ac}+\frac{c(a^2+b^2-c^2)}{2ab}\right)=$$
$$\frac{R\cdot16(a+b-c)(a+b+c)(a+c-b)(b+c-a)}{16abc}=\frac{16R}{(abc)^2}\cdot A^2=\frac{16R}{(abc)^2}\cdot \... | https://math.stackexchange.com |
4,503,516 | [
"https://math.stackexchange.com/questions/4503516",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/1068856/"
] | Perhaps a rather silly question but what exactly is the difference between a non-integral number and a non-integer number?
I have heard both being used but I can't really make out the difference between the two.
Is a non-integral number something concerning integrals?
| Some people call integers integral numbers, but it is not very common. Usually you call "integer numbers" just integers, so you say 2 is an integer, 1/2 is not an integer.
| To echo Dietrich Burde's comment, the phrase “integral solutions” (i.e., solutions that are integers) is rather common in number theory.
I find myself going out of my way to avoid writing the word “integral” to refer to integers—opting for “integer solutions”, for example, instead—because I irrationally worry that the ... | https://math.stackexchange.com |
2,384,797 | [
"https://math.stackexchange.com/questions/2384797",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/225628/"
] | I've been stuck on this problem for quite a while, not sure how to proceed.
<blockquote>
Show that there exists a constant <span class="math-container">$C > 0$</span>, such that for every <span class="math-container">$n \in \mathbb{N}$</span>:
<span class="math-container">$$\frac{n^2}{e^n} \leq \frac{C}{n^2}$$</span... | <strong>Hint:</strong> Find the maximum of the function $$f(x)=x^4e^{-x}$$
You should get that any $$C \geq \frac{4^4}{e^4}$$ is a solution.
| Since
$$e^n = \sum_{k=0}^\infty \frac{n^k}{k!} > \frac{n^4}{4!},$$
the inequality with $C=4!$ falls right out.
| https://math.stackexchange.com |
622,960 | [
"https://physics.stackexchange.com/questions/622960",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/230132/"
] | A long-wavelength, e.g. radio frequencies, of say, 1 km, has a period lasting about 1/300000th of a second.
So for an imaginary fixed observer watching the incoming wave, it takes some time to go from one peak to the next (not saying this measurement is actually feasible).
Also, I would believe the generation itself of... | The essence of this is owing to the time--frequency relationship that is involved in Fourier analysis.
Suppose we have a process that can in principle put energy into the electromagnetic field. In photon language, this is a process that can create photons. If the process can move the field from its ground state to a st... | You are simply assuming that radiation (production of "light" by accelerating charges) produces point-like particles. This is not the case. When we have this sort of radiation the picture that best describes the output is a wave, having said that, this implies there is no localization, the wave itself is an E... | https://physics.stackexchange.com |
2,217,497 | [
"https://math.stackexchange.com/questions/2217497",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/446286/"
] | Let $S$ = the set of all values $n$<100 satisfying that<br>
$ 4^n+3^n+2^n+1^n $
is a multiple of 3<br>
How many values in $S$ are there?
my attempt to solve was about substitution of $n$ values , and i noticed that the only the even ones work
i.e $n$ = 2,4,6,.....
is there any way to prove that ?
| Let's take modulo 3 of the expression. If you are not familiar with modular arithmetic, you should probably look it up as it is integral to solving this problem.
$$4^n + 3^n + 2^n + 1^n \equiv 1^n + 0^n + 2^n + 1^n \equiv 2^n + 2 \mod 3$$
Now we find for which values $2^n \equiv 1 \mod 3$.
$$2^1 \equiv 2 \mod 3$$
$$2^2... | <em>Hint:</em> $4^n+3^n+2^n+1^n \equiv 2^n + 2\equiv (-1)^n-1\bmod 3$ for $n\ge 1$.
| https://math.stackexchange.com |
603,624 | [
"https://electronics.stackexchange.com/questions/603624",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/301878/"
] | In a cave we are exploring we are currently blocked by a small siphon, which we would like to empty into another gallery.
For this, I would like to use a 12 V pump (not selected yet).
As a power source, we would like to use the 36 V Li-ion batteries from our big hammer-drill.
I see 2 options:
<ol>
<li>Using a DC-DC con... | With 48 V PWM on a brushed motor you are going to get 4 times the resistive and eddy current heating you would have gotten with direct 12 V drive. That might be OK, or it might not.
With 48 V PWM on a 12 V brushless motor, it will break immediately.
I'd recommend a DC-DC converter; one with an output current limit may ... | <blockquote>
For option 1, is there any precaution to be taken because the load is inductive rather than resistive?
</blockquote>
Not really, as long as the DC-DC converter can handle the motor´s starting current which can be pretty high.
<blockquote>
For option 2 : is it OK to apply such a high voltage on a 12V motor ... | https://electronics.stackexchange.com |
162,765 | [
"https://dba.stackexchange.com/questions/162765",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/3068/"
] | We're rewriting an old application that uses a single table to manage all of its primitive data types using a key/value format. This table contains thousands of miscellanous items, but here's one example of how it stores OS/OS versions:
<pre>
FirstField FirstValue SecondField SecondValue
System OS Cent... | With the intention of describing how you <em>could</em> do this with a hierarchical key/value pairs table, supporting foreign keys, I've built the following tiny test-bed of code that allows exploring how the structure might work.
Do this in tempdb, to avoid killing anything "interesting":
<pre><code>USE tempdb;
IF O... | There are a couple of things that can reduce the number of primitive tables.
One is to group things Logically at a "near-primitive" level. Your example includes OS, OS version, (and could be broken down to OS patch level to capture the Service Packs...). You could build an OS table that includes these primitives group... | https://dba.stackexchange.com |
119,400 | [
"https://physics.stackexchange.com/questions/119400",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/50514/"
] | Consider the following setup:
An accelerometer is placed inside a helicopter, measuring $g$ values along three axes $(x,y,z)$ every $10~\text{ms}$ (100 times a second), during a helicopter flight.
If one wants to obtain some measure of the maximum $g$ force exerted on an object inside the helicopter, what would be th... | Yes it is. The map you consider acts as follows by definition. $SU(2) \ni U \mapsto R(U) \in SO(3)$ such that
$$U \frac{1}{2}\left(I + \vec{v}\cdot \vec{\sigma} \right)U^\dagger = \frac{1}{2}\left(I + R(U)\vec{v}\cdot \vec{\sigma} \right)\quad \forall \vec{v} \in \mathbb S^2$$
($R(U)$ is a rotation as it is linear and ... | I might be lacking the mathematical depth you desire.
The map $\pi\circ U$ indeed is a rotation. $U$ can be decomposed in terms to the basis given by the Pauli matrices, $X,Y,Z$ and the identity $I$:
$U=\exp(-i\theta \hat n\cdot\vec\sigma/2) = \cos(\theta/2)I-i\sin(\theta/2)(n_xX+n_yY+n_zZ)$
where $\hat n$ is a unit... | https://physics.stackexchange.com |
18,054 | [
"https://security.stackexchange.com/questions/18054",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/11909/"
] | I rent a web server ("service") at a web hosting site which recently i assume got hacked but i am unsure how... I know it got hacked because recently out of the blue certain files and folder appeared on the FTP-server. I deleted all the files and changed the password on everything in relation with this server... a coup... | That's the kind of behavior a botnet displays. What you can assume from the re-appearance of deleted files is that your server has been 'back-doored'.
Changing passwords will not help. A total wipe and rebuild of the server is in order. Because you are 'renting' the service, you will need to shut it down and get a new... | This is a common technique to distribute exploits and viruses: hack a random website, host the data you want to distribute, and make many people go there. Or use the server as update server for a virus that has already spread. This makes it much harder to trace back who wrote the virus.
What I would do is:
<ol>
<li>R... | https://security.stackexchange.com |
24,773 | [
"https://mathoverflow.net/questions/24773",
"https://mathoverflow.net",
"https://mathoverflow.net/users/3664/"
] | This is a question that I have seen asked passively in comments relating to the separation of category theory from set theory, but I haven't seen it addressed in full.
I know that it's possible to formulate category theory within set theory while still being albe to construct the useful things one would want from cate... | I don't agree that this is what (most) categorists who are interested in foundations are doing.
It is true that Lawvere in the mid-60's (and perhaps to this day) wanted to develop a theory of categories independent of a theory of sets, but I don't think that represents the main thrust of modern-day categorical work o... | I honestly think that "naive category theory" (analogous to "naive set theory") <em>helps</em> me understand/remember/do mathematics far more than does set theory. And, since I do not intend to do "formal" category theory, I do not worry about its foundations.
I have some understanding of the Lawvere foundational prog... | https://mathoverflow.net |
18,734 | [
"https://security.stackexchange.com/questions/18734",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/11710/"
] | I'm working on a site which allows users to sign up for a service. They choose a username/password, enter their personal details, etc and proceed into the site, their details being stored for future visits.
Currently, we don't ask for confirmation of the user's email address like most websites do.
The main function ... | You will want to be sure that a user's e-mail address is correct if you intend to send mail to it that is either:
<ul>
<li>security-sensitive (eg forgotten password reset token), or</li>
<li>recurring/high-quantity, to avoid harassing some other person whose address has been entered.</li>
</ul>
This is typically more... | If you plan on <strong>sending email</strong> to that address then you need to verify to avoid being identified as a spammer.
If you ask the user to agree to a <strong>contract</strong> and you can't verify identity based on some other information like a CC#, then you need to verify. If not, then if you ever need to ... | https://security.stackexchange.com |
535,184 | [
"https://physics.stackexchange.com/questions/535184",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/255638/"
] | Can a force which is conservative in one frame become non-conservative in another frame. Why/Why not?
Basically what does it mean for work to be zero in closed loop? If I am thinking of coordinates of starting and ending point and they can be changed by translation of frame. But I think this would muddle up a lot of t... | In classical mechanics, forces are frame invariant. Work is not, in general, because trajectories are not frame invariant.
However, definition of conservative forces requires only that <em>in each reference frame</em> the work depends only on the initial and final point. Variation of this value with the change of re... | No mathematics from my side, but here is what my argument is.
One everyday life conservative force is gravity. Suppose you and your friend are diving side by side in your cars (which can fly). For the time being neglect friction and assume earth to be flat. From the perspective of a observer standing on ground botheri... | https://physics.stackexchange.com |
204,764 | [
"https://mathoverflow.net/questions/204764",
"https://mathoverflow.net",
"https://mathoverflow.net/users/61426/"
] | For $r > 0$, define $f(n) = \lfloor {nr}\rfloor$ if $n$ is odd and $f(n) = \lfloor {n/r}\rfloor$ if $n$ is even. For which real numbers $r$ is the set $\{n,f(n), f(f(n)),\dots\}$ bounded for every nonnegative integer $n$?
So far, I have only computer-generated evidence. If $r = \sqrt 3$, the iterates reach $1$ fo... | Let me write the iteration as $x(k+1, r) = f(x(k,r)) =\lfloor r x(k,r) \rfloor$ if $x(k,r)$ is odd, $\lfloor x(k,r)/r \rfloor$ if $x(k,r)$ is even,
where $x(0,r) = 1$ (for convenience). I claim there is an uncountable set of $r$ for which all $x(k,r)$ are odd, and in particular $x(k,r) \to \infty$ as $k \to \infty$. T... | It's easy to prove that for $r=3+2\sqrt{2}$ and for $n=1$ or $n=3$ the sequences of iterates diverge (as they satisfy some simple recursive relation).
| https://mathoverflow.net |
56,934 | [
"https://dba.stackexchange.com/questions/56934",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/18806/"
] | I'm about to develop an application that will mainly store user-encrypted data. Each piece of data being encrypted thanks to an AES key, itself encrypted with the public RSA key of each granted user.
Given that the volume of non-encrypted data is negligible (probably only users login, some dates and foreign keys), I w... | As a rule of thumb: If your data is well structured, well known (in advance) and of a limited size per entry (no mega BLOBs), relational databases are really good at storing it. Even if you don't use the advanced indexing features.
Managing space, especially empty space in data files, is a very hard problem to solve. ... | There isn't enough information in the question to make an informed decision, but here are some basic points. If you want more detail, please explain more about how the data is going to be queried and how large is it expected to grow, and how large are encrypted segments supposed to be and so on.
So, in general - r... | https://dba.stackexchange.com |
74,300 | [
"https://cs.stackexchange.com/questions/74300",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/46707/"
] | I am trying to use BNF to describe its own grammar to get used to it. What I can not find any information about is whether BNF must consist of <strong><em>zero or more rules</em></strong> or <strong><em>one or more rules</em></strong>. The difference would be:
<pre><code><grammar> ::= <grammar> <rule>... | Concretely speaking, the Backus-Naur form is a notation for context-free grammars, applied to the (formal) description of languages at the syntactical level.
While there are extended versions of BNF that have been standardized, the BNF itself hasn't, so there is no way of determining if the empty grammar is "legal" BN... | There is nothing logically wrong with allowing a grammar to have zero rules. But such a grammar would be entirely useless, as it would not define any language (not even the empty-string by itself).
| https://cs.stackexchange.com |
358,501 | [
"https://softwareengineering.stackexchange.com/questions/358501",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/145346/"
] | Let's say I start developing a role game with characters that attack other characters and that kind of stuff.
Applying TDD, I make some test cases to test the logic inside <code>Character.receiveAttack(Int)</code> method. Something like this:
<pre><code>@Test
fun healthIsReducedWhenCharacterIsAttacked() {
val c ... | In TDD, the tests serve as executable documentation of your design. Your design changed, so obviously, your documentation must, too!
Note that, in TDD, the only way in which the <code>attack</code> method could have appeared, is as the result of making a failing test pass. Which means, <code>attack</code> is being tes... | If the method is complex enough to need testing, it should be public in some class. So you refactor from:
<pre><code>public class X {
private int complexity(...) {
...
}
public void somethingElse() {
int c = complexity(...);
}
}
</code></pre>
to:
<pre><code>public class Complexity {
public int calc... | https://softwareengineering.stackexchange.com |
237,761 | [
"https://softwareengineering.stackexchange.com/questions/237761",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/38401/"
] | I'm interested in building verifications into a REST service to help with service monitoring.
For example, one could run assertions like <code>http://example.com/posts/verify?min-posts=5&since=1-hour-ago</code> which would respond with an error unless 5 new posts had been created in the past hour.
Are there any e... | Supposing you were to ask for the same verification twice in a row. Would you get the same answer? Would it significantly affect the state of the resources? If you are logically going to get the same answer (which doesn't need to be byte-identical, but rather just “the same” in some higher-level sense) and won't be aff... | I don't exactly understand your specific example, but I'll still try to give my advice.
REST is all about entities, or state, and state transitions. It kinda seems like what you want to do is query for some state. Let's look at the common HTTP verbs:
POST
- Commonly used for creating additional state on the server.
... | https://softwareengineering.stackexchange.com |
55,536 | [
"https://mechanics.stackexchange.com/questions/55536",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/38647/"
] | Sorry if its a funny question.
This is my first car so please forgive me if this is stupid question.
Just want to know is it nessecarry to switch on & off the manual ac everytime the vehicle is switched on and off or is it okay to operate it with the key,That is let it be switched on always so it starts & ... | If you operate the AC just with the ignition key condensation might accumulate in the vents, because the ventilation stops immediately after the AC is turned off. That is why some car manuals (mine does) recommend turning off the AC some time before you turn off the engine, such that the ventilation will continue runni... | I leave mine set to on all the time - in fact that is what is advised in the owner's manual for my car, it won't hurt anything.
If you want to switch it off, then that won't hurt either...
| https://mechanics.stackexchange.com |
63,862 | [
"https://mathoverflow.net/questions/63862",
"https://mathoverflow.net",
"https://mathoverflow.net/users/2544/"
] | A friend of mine recently explained to me a little bit about using Lie groups and symmetries to obtain solutions of PDEs. I was interested and wanted to learn a bit more about it. He's been using Olver's "Applications of Lie Groups to Differential Equations" but I found it a bit out of my reach.
I've taken a PDE cours... | I found a solid background in PDE, together with some physics, to be a useful entry point to Olver's nice book. There's the 'Lectures on Partial Differential Equations' by V.I.Arnold which is fun to read alongside, if not before. Any solid book on mathematical methods in classical mechanics and quantum mechanics shoul... | Just to advocate the relevance of groups in PDEs.
<ul>
<li>On the one hand, when a PDE admits a group of symmetries (often translations, rotations, but also Galilean transformation or conformal transformation, ...) you may look for special solutions that behave well under some subgroup (they are invariant or equi-vari... | https://mathoverflow.net |
539,905 | [
"https://electronics.stackexchange.com/questions/539905",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/207355/"
] | I am currently studying <em>The Art of Electronics</em>, third edition, by Horowitz and Hill. Exercise 1.6 says the following:
<blockquote>
<strong>C. Power in resistors</strong><br />
The power dissipated by a resistor (or any other device) is <span class="math-container">\$P = IV\$</span>. Using Ohm’s law, you can ge... | It is important here that you differentiate between the power dissipation (losses) in the wire and the power that is still available for the consumer. The power that is supposed to be available for the consumer is provided: <span class="math-container">$$P_{load} = 10^{10}\; \text{W}$$</span>
You are also provided with... | What you have done is applied 115 volts across the 1 foot of copper cable. This isn't what we are doing here. What you need to find is the amount of current through the cable, but you obtain that by calculating from the power and the voltage. Since P=EI, I will be P/E. When you get done, you can also find I*R, and ... | https://electronics.stackexchange.com |
123,793 | [
"https://physics.stackexchange.com/questions/123793",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/52992/"
] | In proving the total energy in conservative field is constant we have this equation(picture) why it added partial derivative? Why? I mean where it did come from?
<img src="https://i.stack.imgur.com/xkrx5.png" alt="enter image description here">
| The function $U = U(x_1, x_2, \dots x_k, t)$ would be an example of a potential energy function explicitly dependent on time. In your case, you have the function $U = U(x_1, x_2,\dots x_k)$, where it is understood that for each $x_i,\, i \in \left\{1,\dots k\right\}$, we have an implicit dependence $x_i = x_i(t)$. Th... | Lets make up an example.
$$U(x,y,z,t) = E_0\left(x^2+y^2+\alpha\,z^4 -\beta\,t\,z^2\right)$$
In that case parital derivatives are:
$$\frac{\partial U}{\partial x} = 2xE_0,\;
\frac{\partial U}{\partial x} = 2yE_0,\;
\frac{\partial U}{\partial z} = \left(4\alpha z^3 -2\beta z\right)E_0,\;
\frac{\partial U}{\partial... | https://physics.stackexchange.com |
254,420 | [
"https://stats.stackexchange.com/questions/254420",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/76833/"
] | Let $f$, $g$ and $h$ be densities and suppose you have $x_i \sim h$, $i \in \mathbb{N}$. What happens to the likelihood ratio
$$
\prod_{i=1}^n \frac{f(x_i)}{g(x_i)}
$$
as $n \rightarrow \infty$ ? (Does it converge? To what?)
For instance, we may assume $h = g$. The general case is also of interest.
| If one takes the logarithm of this product,
$${\mathfrak{r}}=\log \prod_{i=1}^n \frac{f(x_i)}{g(x_i)} = \sum_{i=1}^n \log\frac{f(x_i)}{g(x_i)}$$and turns it into an average
$$\bar{\mathfrak{r}}_n=\frac{1}{n}\sum_{i=1}^n \log\frac{f(x_i)}{g(x_i)}$$the law of large numbers applies, hence one gets the almost sure converge... | Let <span class="math-container">$Z_n = \prod^n_i \frac{p(x)}{q(x)}$</span>. Consider the quantity
<span class="math-container">$$W_n = \frac{1}{n}log(Z_n) = \frac{1}{n}\sum_i^n log(\frac{p(x)}{q(x)})$$</span>
By Strong Law of Large Numbers,
<span class="math-container">$$\lim_{n \rightarrow \infty} W_n = E_{q(x)}[log... | https://stats.stackexchange.com |
86,703 | [
"https://electronics.stackexchange.com/questions/86703",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/29043/"
] | When I record audio from the line-in jack on my laptop, what function of voltage produces recorded amplitude?
<strong>followup/example</strong>:
Since I've been told "voltage", unqualified: I apply a voltage square wave to a mono cable. (tip-sleeve switches between 0V and +5V every second). Since the voltage as a fun... | You are recording voltage (1V p-p for line level) over time. The line signal is high pass filtered before the voltage sampling by the ac coupling capacitor. Ideally it is also low pass filtered by an anti aliasing filter.
If your square wave had higher frequency (say, 440 Hz) then it would show the voltage sampling be... | An audio signal is just a waveform. The Y-axis is <strong>voltage</strong> or <strong>amplitude</strong>.
The number of times that the waveform is sampled per second is the analog-to-digital converter (ADC) <strong>sampling frequency</strong> (for example 22kHz or 44kHz, etc.)
| https://electronics.stackexchange.com |
224,968 | [
"https://security.stackexchange.com/questions/224968",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/143641/"
] | I would like to understand how firewalls work in details, and understand the attack surface.
<strong>TCP and UDP</strong>
I understand that TCP and UDP are easy to filter. Programs on a computer need to ask the OS to open a port and will listen to these ports. Firewalls can simply look at all incoming packets, check ... | You asked three questions:
<ol>
<li>Requested general understanding of firewalls</li>
<li>How do stateful firewalls protect against non-udp-tcp protocols?</li>
<li>Can data exfiltration occur over non-udp-tcp protocols?</li>
</ol>
<strong>Understanding firewalls background</strong>
Firewalls (as opposed to routers w... | TCP and UDP are layer 4 (transport protocols), and ports are an addressing feature particular to them. There are many other protocols, and they do not use ports. While malware often uses TCP or UDP, mostly to "hide" among normal traffic, it can use other protocols, or even one that the malware writers created on thei... | https://security.stackexchange.com |
194,223 | [
"https://electronics.stackexchange.com/questions/194223",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/25271/"
] | Does changing the input frequency of a transformer rectifier change the output voltage, given that the input voltage is constant with no voltage regulator or protection circuit on the output?
| Assuming all components are perfect, and there are no other components involved, the answer is no.
However, you will usually have an output filter/resevoir capacitor. If the input frequency is increased, this will droop less between half-cycles, and so increase output voltage slightly.
The transformer may have a low ... | Assuming a basic system consisting of transformer, rectifier and output filter, we can make the following considerations:
<h2>The transformer</h2>
Transformers made to operate at line frequency, having a magnetic core (an iron-silicon alloy) material, which can accept a magnetic flux density of about 15000 Gauss or l... | https://electronics.stackexchange.com |
16,261 | [
"https://chemistry.stackexchange.com/questions/16261",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/7835/"
] | I would like to ask if anyone has a list or knows which covalent compounds have metals in them. For example, beryllium and aluminium are both metals but they bond covalently with chlorine to form beryllium chloride and aluminium chloride respectively. Other than these 2 compounds, I do not know any other and thus would... | There is no sharp line between ionic, metallic or covalent bonds.
Most of transition metal oxides and sulfates have strong covalent characteristics. For example, the whole reason of using ligand field theory instead of crystal field theory is that the ionic description (CFT) breaks down, and the covalent effects are ... | There are examples of metal compounds that are regarded by a majority of chemists as covalent in organometallic chemistry. The problem is that not everyone regards some of these compounds as covalent, because the border between ionic and covalent isn't so strict and it doesn't matter.
Alkyllithium compounds and Grigna... | https://chemistry.stackexchange.com |
13,650 | [
"https://dba.stackexchange.com/questions/13650",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/113359/"
] | Does SQL Server execute queries in parallel?
In other words, if I run a heavy query that takes 10 seconds to execute, and at the same time start another heavy query that takes 10 seconds, will the second query actually start after 10 seconds, or will they start both at the same time?
| You mean "concurrently". The answer is yes, with caveats that are too broad to discuss here.
In fact, the whole point of RDBMS is concurrency.
"Parallel" has a precise meaning in SQL Server: "a single query is distributed over more than one processor core".
| As long as your first query doesn't lock a table needed in your second query, they will run in parallel.
| https://dba.stackexchange.com |
88,558 | [
"https://physics.stackexchange.com/questions/88558",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/29111/"
] | I am having a bit of a tough time understanding the following:
<pre><code>|____O____| <- 0A
|____O____| <- 12A
|____O____| <- 24A
| | <- 36A
|_[|||||]_| <- 36A
Legend:
O - A small lamp with 1Ω resistance.
[|||||] - A 12V battery.
</code></pre>
There is 12V flowing across each of the l... | The analogy is wrong. A voltage source can only shock us if it is able to pass a considerable amount of current through our body ( ~ 250 mA or so, I dont know the exact value but you can Google it ). The circuit that you are trying to discuss, does indeed have 36 Amps of current flowing through it, but once you connect... | You're correct in that the overall current is 36A, 12A flowing through each.
So yes, if you physically laid it out as you have drawn, there would wires carrying 36A, a small portion carrying 24, and the individual lamps would each be drawing 12.
It is possible to delivery a small electric shock with a battery, but it ... | https://physics.stackexchange.com |
1,557,508 | [
"https://math.stackexchange.com/questions/1557508",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/295413/"
] | Let $a_n$ be the number of words of length $n$ containing only letters “X” and “Y” without two consecutive “Y”. For example, $a_3 = 5$ since there are exactly five such words:
$$\mathrm{XXX, XXY, XYX, YXX, YXY}$$
I know $a_1=2$ because it can be X or Y, and that $a_2=3$ because it can be XY or XX or YX.
But I do not... | The identity element for $\odot$ is 0. The identity element for $\oplus$ is -1. This is pretty easy to check. Once you have this, it's easy to check that the $\oplus$-inverse of $b$ is $-b-2$. The fact that it's a ring then follows from a tedious but straightforward verification that I'll leave to you.
Edit: How did I... | We could check one by one whether the properties that define a ring hold, starting with associativity of addition and multiplication. Each verification is mechanical, but there are quite a few to do. Painful!
Or else let our new structure be $R^\ast$. Define a mapping $\varphi$ from $R$ to $R^\ast$ by $\varphi(x)=x-1... | https://math.stackexchange.com |
710,887 | [
"https://physics.stackexchange.com/questions/710887",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/186828/"
] | <strong>Is the Lorentz Force involved when the EM wave intersects the receiving antenna? I.e. induces EMF on electrons in the antenna conductor?</strong>
I use the RHR with index finger <span class="math-container">$\vec v$</span> pointing in the direction of wave propagation towards antenna, middle finger <span class=... | The usual way to model a small dipole receiving antenna is as an electrostatic probe sensing the electric field. Small loop antennas are modeled as sensing the EMF due to the magnetic field.
However, you should note that the way we understand the incoming wave is that the electric field excites the magnetic field, and ... | Why have you put V as the velocity of the wave? You're misunderstanding what the right hand rule represents.
The right hand rule, is a tool that is used to visually represent the cross product.
The most common application is to find the magnetic force on a charge,
<span class="math-container">$\vec{F}_{B} = q (\vec{v}... | https://physics.stackexchange.com |
231,960 | [
"https://mathoverflow.net/questions/231960",
"https://mathoverflow.net",
"https://mathoverflow.net/users/88064/"
] | I didn't succeed to find an algorithm that finds the shortest path in a weighted non directed graph between all pairs of nodes whose shortest path distance are inferior to a specific number. I think that, especially if the maximum distance is very small, it should significantly improve my algorithm's performance. Do yo... | It is not clear what you mean by "enclosed by". If this is just the set of points where $f_i(x)>\lambda$, then the answer is "yes", since $$\int_\Omega fdx=\int_0^\infty A(\lambda)d\lambda.$$ This is just Fubuni's theorem applied to the subgraph of $f$.
| Yes, of course, if the word "enclosed" is understood properly. This follows from the definition of Lebesgue's integral. Lebesgue's original definition was the following: this is the limit of sums
<span class="math-container">$$\sum\lambda_j\mathrm{area}\{ x:\lambda_j<f\leq \lambda_{j+1}\}.$$</span>
| https://mathoverflow.net |
4,009,384 | [
"https://math.stackexchange.com/questions/4009384",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/850628/"
] | First statement: <span class="math-container">$F(x)=F(-x)$</span> for every x. <br> <br>
I don't understand why this is false, thinking about the area under the graph of <span class="math-container">$\cos(t^2)$</span>, it would be equal from both sides and symmetric according to <span class="math-container">$x=0$</span... | (1) An easy calculation shows your function is odd and not even:
<span class="math-container">$$F(-x)= \int_0^{-x^3} \cos(t^2)dt =-\int_0^{x^3}\cos(t^2) dt = -F(x)$$</span>
where the middle equality follows because <span class="math-container">$t \mapsto \cos(t^2)$</span> is an even function.
(2) <span class="math-cont... | 1.- For <span class="math-container">$x>0$</span>, <span class="math-container">$-x^3<0$</span>, so <span class="math-container">$$F(-x)=\int_0^{-x^3}\cos(t^2)dt=-\int_{-x^3}^0\cos(t^2)dt \overset{(*)}{=}-\int_0^{x^3}\cos(t^2)dt=-F(x),$$</span> where in (*) we have used that <span class="math-container">$\cos(t^2... | https://math.stackexchange.com |
52,252 | [
"https://engineering.stackexchange.com/questions/52252",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/38996/"
] | Pacjeka states the following on his introduction to tire characteristics:
<blockquote>
The upright wheel rolling freely, that is without applying a driving
torque, over a flat level road surface along a straight line at zero
side slip, may be defined as the starting situation with all
components of slip equal to zero. ... | Even though You ask for no calculations a simple equation is helpful here.
A mass, m at a C.G. height, H, on a stand with base, B needs a force, F to topple.
<span class="math-container">$$F\geq \frac{m*B}{2H}$$</span>
So if the quantity of <span class="math-container">$m/H$</span> decreases the stand is less stable if... | It will require less force to topple the lighter TV. But a lower center of gravity will mean that the whole stand can tip over more before it actually falls. If the center of mass was already high, then 2-3 inches won't be that different. If the center of mass is already relatively low then those 2-3 inches will make i... | https://engineering.stackexchange.com |
322,579 | [
"https://electronics.stackexchange.com/questions/322579",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/143035/"
] | I am using TIM1 to drive a DMA channel which is sending bytes to GPIOF on an STM32F407. TIM1 is started by an OC channel on a different timer. In the DMA stream interrupt handler, I am attempting to stop TIM1 and also reset the counter by generating an Update event. For troubleshooting purposes I have configured an OC ... | It appears that clearing the enabled flag has no effect when the timer is in slave mode.
I have changed my interrupt handler as follows, and now it is working as expected. The timer is stopped and reset, until started again by TIM5.
<pre><code>// Clear interrupt flags
DMA2->HIFCR = DMA_HIFCR_CTCIF5 | DMA_HIFCR_CHTI... | <ol>
<li>it is generally a (very very) bad practice to loop around in an isr.</li>
<li>no point in looping around to clear CEN. if it comes back set, somewhere else your code did it.</li>
<li>flip a pin in the isr to see timing.</li>
</ol>
| https://electronics.stackexchange.com |
280,548 | [
"https://softwareengineering.stackexchange.com/questions/280548",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/123656/"
] | Life, the work day, and personal projects don't always give us the opportunity the commit code at a logical completion (functionality subset programmed, bug fix completely patched, etc.).
Sometimes we need to <em>stop working</em> half way through a new method, or through a half-baked fix. Think... The work day ends, ... | Committing code is cheap in <code>git</code>. You have several options:
<h3>Commit and amend later</h3>
<pre><code> $ git commit --all -m "WIP: half-implemented hack"
</code></pre>
... time passes ...
<pre><code> $ # back to work
$ git commit --all --amend -m "Nice logical atomic commit"
</code></pre>
<h... | Commit away. Commit as often as possible. Commit when its incomplete, commit when its finished. It really doesn't matter. I even will commit and push to remote when I get up for a 1 hour meeting or lunch even...
The catch is you need to be in your own branch (one that no one else will be pulling from). This should be ... | https://softwareengineering.stackexchange.com |
255,117 | [
"https://dba.stackexchange.com/questions/255117",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/196679/"
] | On a (owned) shared server sometimes mysql writes alott of .mad and .mai.
This happens since i think 2 or 3 months, completely random.
It may happen 3 times a day, then it does not happen for a couple of weeks and then on a monday morning the issue occurs again.
It writes alott of files quickly. The disk is full very... | Files like <code>#sql_*</code> are temp files used by things like <code>ALTER TABLE</code>. When successfully finished they are removed. So, I conclude that and <code>ALTER</code> (or some other admin query) was rudely aborted (such as with a crash).
They can safely be deleted.
You 'should' switch to InnoDB.
| To show the engines which can be used by MySQL:
<pre><code>show engines;
</code></pre>
To list all tables, and the engine they use:
<pre><code>select
TABLE_SCHEMA, TABLE_NAME, ENGINE
from information_schema.tables
</code></pre>
These settings for storage engines should also be noted:
<pre><code>show variables li... | https://dba.stackexchange.com |
5,477 | [
"https://earthscience.stackexchange.com/questions/5477",
"https://earthscience.stackexchange.com",
"https://earthscience.stackexchange.com/users/1034/"
] | I have heard the claim by creationists that geologists date rocks by the fossils they contain and date fossils by the rocks in which they are found. This supposedly invalidates radiometric ages because they are a result of circular reasoning. Is this statement purely wrong, or is there some truth to it?
| Yes, there is some amount of circular reasoning in the statement: "<em>geologist date rocks by the fossils they contain and date fossils by the rocks in which they are found</em>".
However, that statement does not fully describe how geologists date rocks or fossils. Dating rocks by fossils is a branch of geology calle... | In addition to what @Michael said, one can add that the claim that "geologist date rocks by the fossils they contain and date fossils by the rocks in which they are found" is misleading: are some rocks being dated using fossils? Yes. Are some fossils being dated by the rock they are contained in? Yes. But they are not ... | https://earthscience.stackexchange.com |
17,211 | [
"https://chemistry.stackexchange.com/questions/17211",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/8231/"
] | In other words, I want to know why some reactions attain equilibrium early in the reaction while some reactions obtain equilibrium at the end of the reaction.
Why is this the case?
| If you define early or end of reaction by the how much the concentration of reactants change from initial reaction to once equilibrium is reached, it is because the equilibrium constant itself is essentially a ratio of the forward and reverse rate constants (can be approximated by the Arrhenius equation posted by t.c.)... | The rate of reaction is dependent on the rate constant, as well as the order of reaction.
The rate constant, which is approximated by the Arrhenius equation, is dependent on the Activation energy, Ea, and temperature, T. Activation energy can be lowered by using a catalyst (if any).
$$k = A e^{-E_a/(R T)}$$
From thi... | https://chemistry.stackexchange.com |
80,620 | [
"https://dba.stackexchange.com/questions/80620",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/50630/"
] | I would like to simulate putting postgresql into "recovery mode".
Few times i have situation where postgresql puted himself into recovery mode. In logs i had:
Oct 18 06:37:35 xx postgres[5738]: [19-1] 2014-10-18 06:37:35.441 CEST|5738|xx|yy|FATAL: the database system is in recovery mode
It was caused by oom which ki... | If you want to force PostgreSQL into recovery, you can create a <code>recovery.conf</code> with no <code>restore_command</code> or streaming replication configuration set. Leave <code>hot_standby</code> set to <code>off</code> in <code>postgresql.conf</code>.
Personally I recommend taking a base backup (<code>pg_baseb... | You can put the database into recovery mode by forcing an unclean shutdown of any of the backend processes, other than the postmaster itself. For example, with <code>kill -9</code>.
Yes, PostgreSQL restarts. That is why it going into recovery mode. Recovery mode is a part of starting up again after an unclean shutd... | https://dba.stackexchange.com |
21,205 | [
"https://mathoverflow.net/questions/21205",
"https://mathoverflow.net",
"https://mathoverflow.net/users/-1/"
] | Are there nef divisors D on a complex projective manifold X such that $h^0(X,D)$ is less than or equal to $\dim X$?
Edit: In fact I'm interested in nef line bundles D, not just divisors.
| Here's an interesting example from complex algebraic surfaces: the so called Godeaux surface. This is a surface, $S$ on which the canonical bundle is $ample$ and yet $h^{0}(S,K_{S})=0$.
To construct such an $S$ we start with a quintic, $S'$ in $\mathbb{P}^{3}$ defined by the Fermat form:
$X_{0}^{5}+X_{1}^{5}+X_{2}^{... | If $A$ is a principally polarized abelian variety, and $L$ the line bundle coming form the polarization, then $H^0(A,L)$ is one dimensional.
| https://mathoverflow.net |
136,932 | [
"https://physics.stackexchange.com/questions/136932",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/55748/"
] | A battery of internal resistance 2 Ohms is connected to an external resistance of 10 ohms. The current is .5 A. What is the emf of the battery?
The correct answer is 6.0 V. When I calculated it like a series circuit with 2 resistors I got 6 V for the emf. But I thought the emf did not include the internal resistance, ... | When current flows, inside the source there is always some voltage drop, so the voltage on the terminals is lower than in the static situation.
We model this behaviour by simple model depicted on your picture; we assume that the real source consists of idealized source -| |- that gives the emf and has not resistance,... | If $E$ is the emf (open-circuit voltage) of the battery and $r_s$ is the internal resistance, the equation relating the series current $I_S$ through an external resistance $R_L$ is given by:
$$I_S = \frac{E}{r_s + R_L}$$
Now, the voltage across the battery terminals $V_{BAT}$ is given by
$$V_{BAT} = E - I_S \cdot r_... | https://physics.stackexchange.com |
29,034 | [
"https://electronics.stackexchange.com/questions/29034",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/5273/"
] | When driving a brushless DC motor, which parameters control the speed. Is it the current in the windings, the voltage, or both? What determines the maximum speed? If you drive the windings with PWM, that controls the winding current, correct?
| First let's consider just a ordinary brushed DC motor. The hardware mechanically ensures that the windings are switched (commutated) such that the magnetic field is always trying to pull the motor along. The magnetic field strength is directly proportional to current, so the torque is proportional to current. So at ... | Speed of the brushless DC motor depends on the same parameters as in a brushed DC motor. The speed is directly proportional to the voltage that is applied to the phases (e.g A,B,C incase of a 3 phase motor). The speed of the bldc motor is inversely proportional to the torque on the rotor shaft when it is set up for con... | https://electronics.stackexchange.com |
55,967 | [
"https://dba.stackexchange.com/questions/55967",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/32311/"
] | Question:
I am currently working on a data migration. I need to migrate 2.5 million rows from one InnoDB table to another InnoDB table (with a different setup).
I am using the following syntax to do that:
<pre><code>INSERT `new_table` (`new_column`,`more_columns`)
SELECT `old_column`,`more_old_columns` FROM `old_ta... | You do not want to do one monolithic transaction because if the transaction fails for any reason, mysqld will spend a long time rolling back everything from the undo logs. There are 1023 undo logs in the system tablespace file (a.k.a. ibdata1). Here is what InnoDB looks like:
<img src="https://i.stack.imgur.com/9EcRi.... | It will all fail or it will all be succesfull meaning one giant transaction.
| https://dba.stackexchange.com |
2,327,674 | [
"https://math.stackexchange.com/questions/2327674",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/20236/"
] | Suppose that $f$ is defined on the interval $[a,b]$, where $\;a<b\;$. According to the fundamental theorem of calculus:
$$\frac {d} {dx} \left( \int_{a}^{x}f(t) dt \right) = f(x)$$
What can be said about the following?:
$$\frac {d} {dx} \left( \int_{b}^{x}f(t) dt \right)$$
| If you mean $\;x\in[a,b]\;$ and $\;a<b\;$ , then
$$\frac {d} {dx} \left( \int_{b}^{x}f(t) dt\right)=\frac {d} {dx} \left(- \int_{x}^{b}f(t) dt \right)=-\frac {d} {dx} \left( \int_{x}^{b}f(t) dt \right)=-(-f(x))=f(x)$$
| $$\text{They are equal: }\frac d {dx} \int_a^x f(t)\,dt = \frac d {dx} \int_b^x f(t)\,dt. \tag 1$$<br>
$$ \int_a^x f(t)\,dx = \underbrace{\int_a^b f(t) \,dt}_{\large\text{This is a “constant.''}} + \underbrace{\int_b^x f(t)\,dt.}_{\large\text{This is NOT a “constant.''}} \tag 2$$<br>
<b>“Constant”,</b> in the context... | https://math.stackexchange.com |
407,231 | [
"https://electronics.stackexchange.com/questions/407231",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/204603/"
] | I'm trying to create a PCB filter that will allow me to select everything on the board except for components that have an 0402 or 0603 package size. We have a parameter in our passive parts called "Package" which can be '0402' or '0603', so this would be a perfect way to isolate these components.
I can easily select t... | It looks to me like the power cables are insulated. That's not common in my neck of the woods. If the power was turned off, it was for additional safety.
| Yes, the wires are insulated. It might be due to the congested urbanization. I have been seeing the same thing even here in India, over the last 10 years. Earlier, they used to be bare wires and regularly caused injury to either people carrying long poles etc, or they got torn in cyclones and fell to the ground.
Somet... | https://electronics.stackexchange.com |
159,701 | [
"https://mathoverflow.net/questions/159701",
"https://mathoverflow.net",
"https://mathoverflow.net/users/47937/"
] | Denote by $\mathrm{Hom}$ continuous group homomorphisms. Fix the quotient homomorphism $\mathbb{R}\to S^1$.
Can one characterize those topological (e.g., locally compact, and in particular discrete) groups $G$ such that the induced map $\mathrm{Hom}(G,\mathbb{R})\to\mathrm{Hom}(G,S^1)$ is bijective?
Clearly this ho... | Sasha's argument is pretty technological. You can really do this almost by hand, though.
Let $A$ be the algebra in question, let $r$ be its Jacobson radical (that is, the subspace of strictly upper triangular matrices), and let $E$ be the subalgebra of the diagonal matrices in $A$ (which is a complement to $r$) Notice... | This is the same as Hochschild homology of the derived category of $A$-modules. The derived category has a semiorthogonal decomposition into $n$ components equivalent to the derived category of $K$-modules each. Hochschild homology is additive for semiorthogonal decompositions. Thus $HH_\bullet(A) = K^n$, everything si... | https://mathoverflow.net |
485,498 | [
"https://physics.stackexchange.com/questions/485498",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/204775/"
] | In Special Relativity - Is their a definition of "synchronizing" clocks which are moving relative to each other?
I suspect such a definition makes no sense - as moving clocks belong to separate reference frames and there is no sense is talking about clocks and synchronization outside the context of a particular refer... | How could you synchronize them, when each frame says the clocks in the other frame are running slower? Also, there's no intrinsic chronological order of events that have space-like separation.
| Yes, I believe you are correct. I'm not an expert on relativity, but it is my understanding (from reading Einstein's book "Relativity- The Special and the General Theory) that the main value of synchronizing clocks is for clocks that are within a single inertial frame.
Hope this helps.
| https://physics.stackexchange.com |
103,893 | [
"https://softwareengineering.stackexchange.com/questions/103893",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/31418/"
] | Consider these methods:
<pre><code>public List<Employee> GetAllEmployees()
{
using (Entities entities = new Entities())
{
return entities.Employees.ToList();
}
}
public List<Job> GetAllJobs()
{
using (Entities entities = new Entities())
{
return entities.Jobs.ToList();
... | One idea would be to wrap it with a function that takes a <code>Func</code>.
Something like this
<pre><code>public K UsingT<T,K>(Func<T,K> f) where T:IDisposable,new()
{
using (T t = new T())
{
return f(t);
}
}
</code></pre>
Then your above code becomes
<pre><code>public List<Empl... | To me this would be like worrying about foreach-ing over the same collection multiple times: it's just something that you need to do. Any attempt to abstract it further would make the code much less readable.
| https://softwareengineering.stackexchange.com |
65,595 | [
"https://chemistry.stackexchange.com/questions/65595",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/39450/"
] | I do not understand why you could not fill a bowl full of adenosine triphosphate (ATP) and eat it. Is there a way to make ATP other than inside a cell and apply it to your body by injection, ingestion, topical absorption, inhalation, or another method?
| To answer the question in the title:
Yes, ATP can be synthesised, isolated and you can even eat it. It would be very expensive to do so but considering others put gold on most of their food that’s not a reason in itself not to. While eating too high a dose of ATP is not beneficial as per Paracelsus’ law, small amounts... | Expanding upon the comment above detailing how exogenous ATP isn't that great of an idea given the path of delivery, it's also important to note that our body focuses more on consumption, storage, and mobilization of fuels. The actual ATP production and utilization happens on a cell by cell basis, but fuels are moved a... | https://chemistry.stackexchange.com |
92,825 | [
"https://electronics.stackexchange.com/questions/92825",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/31260/"
] | Is there a way to measure capacitance of a capacitive network as shown below in Tina-TI, Multisim, or other simulators? I tried searching but I couldn't find any way to measure capacitance directly as compared to the DMM in the simulators. Our professor requires Tina-TI, but if it isn't possible, we'll just ask his per... | As far as I know, there is no direct way to measure capacitance in simulators (e.g. capacitance-meter). Please take note that for this project, we were only allowed <strong>DC sources</strong>.
We came to a solution in this problem by implementing what we learned about steady-state response of an RC circuit. As such,... | Step a DC voltage with a fixed output resistance across the terminals. You should be able to do a transient analysis and estimate the time constant of the exponential voltage rise across the network. Time constant = RC, so if you know R, you know C.
If you can't do a step function, you're out of luck. You can't measur... | https://electronics.stackexchange.com |
359,560 | [
"https://physics.stackexchange.com/questions/359560",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/170221/"
] | If the term electrostatic potential energy is used to define the electric potential energy of the <strong>system</strong> and <strong>not</strong> an individiual charge in a closed system of two/more charged particles, how is it possible to find the electric potential energy of an individual charge using V= $\frac{U}{q... | AS @garyp has stated the potential (pun!) for confusion about potential energy can start early in ones education.<br>
It is difficult enough to explain what potential energy is and that is perhaps why the extra layer of sophistication is omitted?
Consider the gravitational potential energy possessed by ball <strong>... | Quite simply, because $V(r)$ is due to the other charge or charges in the system. You can't have a $V$ without a charge to create it.
The potential energy that you calculate using $U=qV$ is the potential energy of the system comprising the charges that create $V$, and the charge who's value is $q$.
| https://physics.stackexchange.com |
38,045 | [
"https://cs.stackexchange.com/questions/38045",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/6689/"
] | Assume we have a (multi)set of nontrivial intervals $\mathcal{I} = \{I_1,...,I_n\}$ and for any two $I_i, I_j \in \mathcal{I}$, we have that $I_i \cap I_j$ is trivial (that is: contains at most one point), or one of them contains the other. Just to clarify, an example would be $\mathcal{I} = \{[0,10], [2,6],[6,8], [2,4... | You can solve it in $O(n \lg n)$ time using a divide-and-conquer algorithm.
<h2>Explaining the main idea: a cleaner variant</h2>
To help me explain the main idea, I'm going to change the problem slightly. I'll assume we're given a set of intervals, with no interval appearing more than once in the set, and where for ... | What about another sorting order, which seems to be compatible with pre-order in your proposed trees?
Define $I \le I'$ with $I=[a,b]$ and $I'=[c,d]$ iff $I$ is before $I'$, i.e., $b\le c$, of $I$ contains $I'$, i.e., $a\le c$ and $d\le b$.
| https://cs.stackexchange.com |
560,408 | [
"https://physics.stackexchange.com/questions/560408",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/157704/"
] | You can think about a paramagnetic material as being comprised of a bunch of quantum mechanical spins aligned in random directions. When an external magnetic field is applied, a fraction of the spins will align with the magnetic field. The stronger the external magnetic field, the larger the number of spins which will ... | You are correct: a tensor can be viewed as a linear function in many different ways. We define a <span class="math-container">$(p,q)$</span> tensor <span class="math-container">$T$</span> as a function that takes <span class="math-container">$p$</span> covectors and <span class="math-container">$q$</span> vectors and r... | Forget tensors for a moment and just think about our old friend the matrix. Take a
square matrix for example. You can multiply it onto a column vector and get back a column vector. Or you can put a row vector to the left and a column vector to the right, multiply them all together, and the outcome is a scalar. This is ... | https://physics.stackexchange.com |
21,728 | [
"https://dsp.stackexchange.com/questions/21728",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/5392/"
] | As I know if the impulse response is symmetric around sample zero phase response should be entirely zero.
The code below just set a rectangular window for vector "in"
<pre><code>const int N = 10;
// in = 0 , 0 , 0 , 0 , 1 , 1 , 1 , 0 , 0 , 0 , 0
std::vector< std::complex<double> > in (N);
std::vector&l... | The problem is that your input vector is <em>not</em> symmetric when considering the definition of the DFT:
$$X[k]=\sum_{n=0}^{N-1}x[n]e^{-j2\pi nk/N}\tag{1}$$
Note that from (1) the time indices start at $n=0$. If you periodically continue the signal $x[n]$ in your example you get
<code>n: ... -5 -4 -3 -2 -1 | 0... | Those are complex conjugates, which when you add give only , the real part. Intuitively exp(jwo)+exp(-jwo). so the resulting phase has the form invtan(imaginary_part/real_part) (invtan is tan inverse function), where b is o. so the phase spectrum will only have zeros.
That is the angles obtained, from a+jb is theta, ... | https://dsp.stackexchange.com |
8,051 | [
"https://cogsci.stackexchange.com/questions/8051",
"https://cogsci.stackexchange.com",
"https://cogsci.stackexchange.com/users/6605/"
] | <strong>Background:</strong><br>
I am a student currently doing my undergraduate degree (Electrical and Electronics, if it interests anyone). I am very much interested in studying psychology. I have read quite a bit on psychology, mostly on PsychCentral and PsychologyToday, but the knowledge I have is in bits and piece... | I’ve compiled a reading list based on the books I acquired during my undergraduate and graduate psychology programs. I’ve not listed the year I took the course because, with the exception of Introduction to Psychology being required first year and History and Systems being required in our last year (History and Systems... | There are hundreds of introductory textbooks out there, not just for psych in general but for the fields in psychology, so choosing a text isn't straightforward. You would be best off asking for an expert opinion from those who have taught intro courses at a university, and then check the ratings on Amazon. For example... | https://cogsci.stackexchange.com |
561,758 | [
"https://electronics.stackexchange.com/questions/561758",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/159693/"
] | I have used those XT60 power connectors to connect from my load to the battery. The battery is a forklift battery with a voltage of 48V.
I have attached the male XT60 connector to the battery pack and the female XT60 connector to the load input via two 2.5mm power cables.
I have also shown a person how to connect the m... | Our forklift uses a MASSIVE Anderson Powerpole connector. Much, much larger than the Powerpoles I use on RC planes.
| You could use fully-insulated quick disconnect terminals with the battery + going to a female terminal and the battery - going to a male terminal, with the mating terminals on your load. It doesn't stop someone from connecting the quick disconnects from the battery to each other, but if you really care about that you ... | https://electronics.stackexchange.com |
3,479,735 | [
"https://math.stackexchange.com/questions/3479735",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/624325/"
] | I am unable to see whether this statement is true or false, any help would be appreciated.
Let <span class="math-container">$E$</span> be the splitting field of a polynomial over <span class="math-container">$\Bbb{Q}$</span> which has both real and complex roots. Then the conjugation automorphism is an element of <sp... | The fixed field of the complex conjugation is <span class="math-container">$M=E\cap\Bbb{R}$</span>, and by Galois theory we always have <span class="math-container">$[E:M]=2$</span>. The field <span class="math-container">$K$</span> generated by the real zeros and the real parts of the complex zeros (which is what you ... | Let <span class="math-container">$\sigma$</span> be the complex conjugation. Write <span class="math-container">$P=\Pi_{i=1}^{i=n} (X-a_i)=P^{\sigma}=\Pi_{i=1}^{i=n} (X-\sigma(a_i))$</span> implies that <span class="math-container">$\sigma$</span> preserve the roots.
| https://math.stackexchange.com |
20,175 | [
"https://security.stackexchange.com/questions/20175",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/1431/"
] | Suppose you're truly paranoid (I assume the majority here identify with this?) and you don't want Google or other email service providers reading your email (to serve ads, etc). You don't want your ISP making backups of your messages (even with good intentions) because when you delete an email, you want it to be <stro... | It's not paranoia if you've conducted a proper analysis and have identified a likelihood that they are out to get you in excess of your acceptable risk threshold.
Running your own server is a fairly reasonable control for the risk that the admin of your mail server reads your mail or is subpoenaed for their backups. Y... | <blockquote>
Is my solution (home mail server) the best for my goal?
</blockquote>
As you've already noted, the email passes through other machines to get to you. And SSMTP is only really supported for MUA to MTA connections.
Unless you have your own domain and a dedicated IP address outside of the main consumer bl... | https://security.stackexchange.com |
517,084 | [
"https://physics.stackexchange.com/questions/517084",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/228914/"
] | I'm trying to understand a proof my lecturer gave. We define <span class="math-container">$\hat{T}(a)=e^{-ia\hat{p}/\hbar}$</span> and write
<span class="math-container">$\hat{x}\hat{T}(a)|x\rangle =\hat{x}(\mathbb{1}-i\frac{a}{\hbar}\hat{p}+\frac{1}{2}(-i\frac{a}{\hbar}\hat{p})^2+\dots)|x\rangle=(\hat{x}-i\frac{a}{\h... | First, yes, in the notation <span class="math-container">$|x\rangle$</span> and <span class="math-container">$|p\rangle$</span> the symbols <span class="math-container">$x$</span> and <span class="math-container">$p$</span> label the eigenvalue of the eigenstate represented by the ket. In that sense <span class="math-c... | There is a new state <span class="math-container">$T(a)|x\rangle$</span> which we name <span class="math-container">$|?\rangle$</span>
Turns out, from your computations, that the eigenvalue of the position operators on <span class="math-container">$|?\rangle$</span> is (a+x) - so we name it with a more meaningful name... | https://physics.stackexchange.com |
1,623,905 | [
"https://math.stackexchange.com/questions/1623905",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/300044/"
] | Prove that $\lim\limits_{n\to\infty}c_n=0$ where $c_n=\frac{a_1b_n+a_2b_{n-1}+\cdots+a_nb_1}{n},\lim\limits_{n\to\infty}a_n=0,|b_n|\le B=\text{const}$. $\{a_n\},\{b_n\},\{c_n\}$ are sequences.
$$c_n=\lim\limits_{n\to\infty}\left(\frac{a_1b_n}{n}+\frac{a_2b_{n-1}}{n}+\cdots+\frac{a_nb_1}{n}\right)=\lim\limits_{n\to\inf... | Since $\text{lim}_{n\rightarrow \infty}a_n=0$ .
Using Cauchy's definition $\forall \epsilon \in \mathbb{R}$ , $\exists N'$ such that for all $n> N'$ ,$a_n<\dfrac{\epsilon}{2 |B|}$
$$|B|\left|\sum_{i=N'}^{n}\dfrac{a_i}{n}\right|< \dfrac{\epsilon} {2}$$
Let $N'=\left\lceil{\dfrac{\text{max}(a_1,a_2,\ldots,a_... | <strong>HINT:</strong>
For any $\epsilon>0$ there exists a number $N>0$ such that whenever $n>N$, $-\epsilon<a_n<\epsilon$.
Now, write the sum as
$$\frac1n \sum_{k=1}^n a_kb_{n-k+1}=\frac1n \sum_{k=1}^Na_kb_{n-k+1}+\frac1n \sum_{k=N+1}^n a_kb_{n-k+1}$$
For the first sum, with fixed $N$, let $n\to \i... | https://math.stackexchange.com |
3,197 | [
"https://quant.stackexchange.com/questions/3197",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/2261/"
] | Rho is the partial derivative of the value of call option, $C$, w.r.t the riskfree interest rate $r$: $$\rho \equiv \frac{\partial C}{\partial r}$$
In the standard B-S formula this term is positive, but <strong>what's the intuition</strong>? I understand that two forces are at hand: one is that as $r$ increases futur... | The main reason that rho term is positive is that we are using arbitrage-free pricing theory. In particular, regardless of model, the value of a forward contract (for an asset paying no dividends) is
$$
F_T = S_0 e^{rT}
$$
Therefore, in <em>whatever</em> option pricing model you choose, the center of its forward ... | Here's the relationship of rho on calls and puts.
When you buy call options instead of the the underlying, you are effectively buying an indirect leveraged position in the underlying. A simple way to see this is buy re-arranging the terms of the Put-Call parity equation solving for the call price. The value of the cal... | https://quant.stackexchange.com |
7,868 | [
"https://math.stackexchange.com/questions/7868",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/-1/"
] | What is the degree of the polynomial of the following expression ?
$$ [x + (x^3 – 1)^{1/2}]^5 + [x – (x^3 – 1)^{1/2}]^5 $$
If I am not very wrong the highest power of x is $\frac {15}{2} $ ?! So the degree is floor(15/2) = 7 ?! The answer is 7 but I am not sure of this approach.
Please comment.
| Usually, a polynomial is understood to have only non-negative powers of $x$ (i.e. $x^0=1,x^1=x,x^2$ etc.), so a-priori it's not even clear that this is a polynomial. However, if we open up the binomial theorem, we see that the odd powers cancel:
\begin{equation*}
(x+y)^n + (x-y)^n = \sum_{k=0}^n \binom{n}{k} x^{n-k} [... | If you expand the 5th powers, the terms that have square roots in them will cancel.
| https://math.stackexchange.com |
56,059 | [
"https://dsp.stackexchange.com/questions/56059",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/41158/"
] | I was hoping to clarify if the following was correct:
<ul>
<li>A real function (neither even nor odd) in time exhibits conjugate symmetry in frequency, so the real part of the frequency response is even, and the imaginary portion is odd</li>
<li>A real, even function has a frequency response that is strictly real and ... | Your suspicion is correct. You can show this as follows:
<span class="math-container">$$X(\omega)=\int_{-\infty}^{\infty}x(t)e^{-j\omega t}dt\tag{1}$$</span>
<span class="math-container">$$X^*(\omega)=\int_{-\infty}^{\infty}x^*(t)e^{j\omega t}dt\tag{2}$$</span>
Now if <span class="math-container">$x(t)$</span> is pu... | Based on
<span class="math-container">\begin{equation}
x(-t) \rightarrow {X}(-\omega) \hspace{1cm} (time-reversal)
\end{equation}</span>
<span class="math-container">\begin{equation}
{x^*}(t) \rightarrow {X^*}(-\omega) \hspace{1cm} (conjugation)
\end{equation}</span>
if we were able to split a function <span class... | https://dsp.stackexchange.com |
399,486 | [
"https://electronics.stackexchange.com/questions/399486",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/200342/"
] | I want to add a relay or transistor, what fits the need best, to a simple switch, so I can control the switch by a micro computer but also keep the already installed switch so I can still operate the mechanism by hand.
Here a little sketch of what I thought of (sorry, I'm new to electronics so forgive me if this is a ... | Your proposed solution works for half the problems. The additional relay (that's what I recommend given the scant information about the load) is logically ORed with the switch. If either is on, then the overall switch is on. For the overall switch to be off, both the original switch and the relay need to be off.
Wi... | You can solve this with a electromechanical or solid state relay, which provides the same function as the switch.
You could also use a simple transistor, but then the polarity of the switch current/voltage must be considered.
| https://electronics.stackexchange.com |
70,493 | [
"https://dsp.stackexchange.com/questions/70493",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/31367/"
] | Can the intelligence message of an FM signal be cross-modulated to a a different frequency by non-linearities, but with the FM modulating message remaining (relatively) intact on the new frequency?
This isn't really trying to solve a particular problem, but I'm trying to understand if this is possible, and if the math... | I don't see any obvious issue with the OP's reasoning except to clarify that the cross-modulation is is not onto another FM signal but onto another FM channel with caveats on intelligibility. Below I add more detailed intuitive explanation as to how this occurs:
If a non-linearity creates a harmonic at <span class="mat... | Yes and no, it can't be intermodded onto another SIGNAL, but it can be intermodded onto another CHANNEL. For example, if you are monitoring 144 MHz, an FM signal on 145 MHz and on 146 MHz CAN, due to non-linearity, end up being heard on 144 MHz. But it can't be modulated onto an existing signal on 144 MHz.
Mark
| https://dsp.stackexchange.com |
100,902 | [
"https://electronics.stackexchange.com/questions/100902",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/37779/"
] | I have this circuit (Power supply is 5V):
<img src="https://i.stack.imgur.com/xijjN.png" alt="CS5530 Circuit">
The problem is: How to convert the values to Volts? I get the digital value in 24-bit from spi interface, but I don't know the minimum and maximun voltages to calculate a conversion.
Thanks.
<hr>
SOLUTION... | The +ref is tied to +5V and the -ref is tied to 0V - this means your input signal range is 5V but, there is an analogue stage with a fixed gain of 64 so this means your input range is 78.125mV.
Additionally the spec sheet says: -
<blockquote>
The common-mode plus signal range of the instrumentation amplifier is
(... | Also using 24bit ADC with Vref hooked up to power practically gives you way lower effective number of bits, so your 24bit ADC becomes 16bit or less due to the noise contamination of Vref input.
Also CS5530 datasheet has calibration section.
| https://electronics.stackexchange.com |
106,361 | [
"https://electronics.stackexchange.com/questions/106361",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/24836/"
] | I know that having TX, RX, GND, RTS, CTS are good. What about all of the others? Do devices these days even make use of the other pins (DSR, RI, DCD, DTR)? Is it safe to generally leave out these pins? It seems to me like these are mostly only used in fully-specified legacy DCE/DTE equipment. FYI I'm asking this questi... | The most basic maneuver for complicated functions is to utilize the onboard timers.
Depending on how you set them up, you can get them to count exactly the number of clock cycles it takes for a certain function to execute. Simply read the timer before the function call and then again after the function call.
You w... | If it is a small function you could just look at the disassembly and count the instructions.
| https://electronics.stackexchange.com |
2,829 | [
"https://softwareengineering.stackexchange.com/questions/2829",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/526/"
] | I originally thought of creative commons when while reading a book about wordpress (professional wordpress), I learned that I should also specify that the product is provided
<blockquote>
... WITHOUT ANY WARRANTY; without even the
implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE
</blockqu... | For small bits of code, I generally release them under the X11 licence. The problem with the GPL is that it's far too complicated for code that you don't really care enough about to protect. If you <em>really</em> don't want people using your code in commercial products, you would need to monitor for infringement and f... | Personally your best bet to get a true answer to this question would be to talk with a Legal Professional as they are going to know the specifics.
However, what I remember when i was talking with my lawyer about setting up our code license agreements is that the clause you are talking about basically protects you from... | https://softwareengineering.stackexchange.com |
7,947 | [
"https://engineering.stackexchange.com/questions/7947",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/77/"
] | I've been looking at solutions to compress gases and getting stunned by the cost and maintenance requirements of existing systems to fill cylinders (whether for SCBA or chemical storage) to 2000-4000psi: The cost of entry is over 4 figures, with commercial systems like those used in fire stations and SCUBA shops runni... | There are two aspects to this. First is that the main advantage of hydraulics is that is provides a compact means of greatly multiplying <em>force</em> but in compressing gasses you have to a huge amount of work on the gas itself so the constraint is the power input so you are always limited by the capacity of the mo... | The elephant in the room is that while gasses are compressible, hydraulic oil is only negligibly so.
This difference has two major effects:
Firstly, the output volume flow is limited by the intake volumetric flow divided by the compression ratio. Let's say we have a hypothetical compressor that pulls in 10 L of air ... | https://engineering.stackexchange.com |
287,445 | [
"https://dba.stackexchange.com/questions/287445",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/162483/"
] | SQL Server automatically handles index fragmentation issue when a certain number of rows are inserted/updated.
Then why is there an option to rebuild/reorganize an index?
| Are you confusing fragmentation with statistics?
There is no auto handling of fragmentation. Do you have some reference to point to?
There is, however, auto update of statistics. It is a bit crude, which is why we might complement it with scheduled stats update jobs.
| The design philosophy of SQL Server is to have most maintenance be automated, but since no automation is perfect, allow manual override for advanced users.
| https://dba.stackexchange.com |
126,303 | [
"https://security.stackexchange.com/questions/126303",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/69917/"
] | I want to set up a firewall for a small office. I have a server on which I can install an OS of my choice. I was thinking of trying pfSense but ran into some testing problems and tried IPFIre (Linux based). Hence I will only be referring to the last one here.
IPFIre is easy and fast to setup via the web interface. Ho... | I've been doing professional pentesting for quite a while covering many of the banks having a permit here in Switzerland. Traditionally they were using <strong>username/password</strong> only.
Then they switched to <strong>TAN</strong> (transaction authentication number) handed out on paper. I just know 2 remaining ba... | I've never heard of just using the date of birth for authentication. It's a bad idea as a date of birth is non-revocable. Meaning if it is "compromised" you can't change it.
If it is the only means of authentication for consulting account or transactions it's a <em>REALLY BAD IDEA</em>.
But that brings me to my sec... | https://security.stackexchange.com |
384,156 | [
"https://mathoverflow.net/questions/384156",
"https://mathoverflow.net",
"https://mathoverflow.net/users/174306/"
] | Let <span class="math-container">$G_0(x)=G(x,0)$</span> be the Green's function of the simple symmetric random walk on <span class="math-container">$\mathbb Z^d$</span>, <span class="math-container">$d\geq 3$</span>. The question is whether <span class="math-container">$G_0$</span> must always vary locally, i.e., wheth... | We will use the elementary fact that for <span class="math-container">$m \ge k \ge m/2$</span>, the binomial coefficients satisfy
<span class="math-container">$${m\choose k+1} <{m \choose k}. \quad (\#)$$</span>
The case <span class="math-container">$x=0$</span> is obvious so we may assume <span class="math-conta... | If e.g. the random walk can only move in the positive direction relative to an oriented hyperplane <span class="math-container">$H$</span> in <span class="math-container">$\mathbb R^d$</span>, then the Green function will be locally <span class="math-container">$0$</span> and hence constant for all points <span class=... | https://mathoverflow.net |
138,898 | [
"https://softwareengineering.stackexchange.com/questions/138898",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/49366/"
] | I'm thinking of some of the array functions. "key", "each", "pos", "range". These are often very useful as local identifiers! I have also seen code that (ab)uses $return, $list, $array, $string. What are other PHP programmers views on this?
Local identifiers only! I wouldn't use them as members or method names of a cl... | The reason they bother me is not because they are reserved words within the language itself, but rather that they are too general. What does the <code>$array</code> contain? What is it an array of?
<code>$list, $string, $array, $key, etc</code> are far too generic and not descriptive enough variable names to be useful... | From your perspective it may seem like they 've stolen your favorite symbol names - and in many occassions this can be said for most programming languages. From a seasoned PHP developer's viewpoint however, these symbols are a solid foundation on which he can be based to produce code with a well - defined behavior - at... | https://softwareengineering.stackexchange.com |
335,353 | [
"https://physics.stackexchange.com/questions/335353",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/156902/"
] | I understand that with an infinite plane, as you get closer, the infinitesimal contributions to the electric field become greater in module. The direction of the vectors become less perpendicular to the plane as you get closer, hence reducing the overall electric field in the perpendicular direction. Both effects offse... | Well, the explanation really is held in Gauss's Law. That shows that the field of an infinite line is distance dependent, while an infinite plane is not.
But I expect you're looking for a more intuitive answer. So I'll give my best shot at one. Keep in mind, that dealing with an infinite anything tends to be non-intui... | Think of electric field lines and how they diverge from a charged wire. Also, think about how field strength is related to the "density" of field lines. Having an infinite plane counteracts this diverging effect as adjacent lines keep the field directed perpendicular to the plane at a constant distance apart.
| https://physics.stackexchange.com |
3,232,782 | [
"https://math.stackexchange.com/questions/3232782",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/661803/"
] | I got that i have 286 (4 digit numbers) that their sum equals 10 , Then I checked 3 invalid cases:
x1 + x2 = 5
x2 + x3 = 5
x3 + x4 = 5
I got that I have 5 options for case 1 (one option less than cases 2-3 , because 0 as a first digit is invalid) , and 6 options each of cases 2-3.
So I need to subtract 286 - 5 - 6*... | You can simply study the linear systems that need to be solved in order to get the coefficients on each base.
(1) obviously works and (4) obviously doesn't work. For instance for (2) what you want to know is if every polynomial <span class="math-container">$a_0+a_1 X + a_2 X^2$</span> can be written in the form <span ... | <strong>Hint:</strong> Since <span class="math-container">$\{1, x, x^2\}$</span> is a basis of <span class="math-container">$P_2(\mathbb{R})$</span>, write your elements in that basis (they already are). Then, form a matrix using the coefficients. They span <span class="math-container">$P_2(\mathbb{R})$</span> iff the ... | https://math.stackexchange.com |
49,394 | [
"https://electronics.stackexchange.com/questions/49394",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/16265/"
] | I was thinking of attaching a sensor to the rope but there are so many types I'm not sure which one to use.
Pizeoelectric, rolling ball, vibration, tilt and tension sensors could all work.
I need the lowest cost, most durable solution. Anyone have any ideas here?
| I'd recommend an opposed-beam optical sensor. PCB-mount varieties can be purchased for around $0.25 in low volumes. Use an extension spring in series with one end of the rope to provide a little compliance (to make it kid proof, keep a length of rope in parallel with the spring so that the spring can only be stretche... | The easiest thing to use is a proximity sensor. These are commonly used as safety mechanisms on machines. You will need to use thin copper wires instead of a string and isolate them from ground. Anyone touching the wire would cause the system to trip. These are frequently used in security to protect products on shelves... | https://electronics.stackexchange.com |
306,687 | [
"https://electronics.stackexchange.com/questions/306687",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/123349/"
] | After realizing the l293d output won't suffice and the voltage drop of the l298 is quite high, I believe learning to construct a simple H-Bridge to suit would be beneficial. Before starting with tests, am I correct in assuming the voltage drop of the below circuit would be calculated by the data sheets Rds(On) of each ... | You are correct about the voltage drops in the mosfets. The only other major factor would be your supply (Vdd) and its ability to source the current without dropping (e.g. if the wire between the bridge and supply is long and or small). The other thing to pay attention to when using the Rds(On) from the datasheet is ... | Don't use resistors!!! There are gate drivers for that. Driving a gate takes sometimea 5A, definitely must be done quickly, not through RC filter (C is the gate). Otherwise you can't do PWM and if you just switch, you risk burning a MOSFET by heat.
| https://electronics.stackexchange.com |
247,325 | [
"https://electronics.stackexchange.com/questions/247325",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/117453/"
] | I want to pass a pin value in user define function in 89c52 code like given below
<pre><code>#include <AT89c52.h>
sbit myBit = P1^5;
void f(sbit recievedBit){
recievedBit = ~recievedBit;
}
void main(){
myBit = 0;
while(1){
f(myBit);
//some delay here
}
}
</code></pre>
But it give me ... | The 8051 processor has a peculiar memory layout, which can be very handy for manipulating bits. In addition to "normal" bit addressing, supported by many processors (location address + bit number), the 8051 has a "bit mode" addressing: a single byte (0-255) can address 256 different bits (in two different areas) with a... | <code>void f(sbit recievedBit){
recievedBit = ~recievedBit;
}</code>
When you call <code>f(myBit)</code> , value of <code>myBit</code> is assigned to local variable <code>recievedBit</code> and in function <code>f</code>, only value of that local variable is toggled. This is called as "Pass by Value". You are pas... | https://electronics.stackexchange.com |
15,148 | [
"https://physics.stackexchange.com/questions/15148",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/5437/"
] | If you were to sink a container to the bottom of a deep ocean and seal it there, then bring it up to the surface, would it retain its pressure?
The answer for a gas is obviously yes, but what about for a liquid like water which is incompressible? Once the crushing weight of the water column above is removed, does the ... | Water is slightly compressible, so it will hold its pressure as long as the container does not stretch.
But since it's only slightly compressible, if the container bursts under pressure it will probably not be an explosive failure. This is because at the time of failure, unlike a gas, the water does not push for a lon... | The problem in your post is that you don't consider the force resisting the water pressure, which is exerted by the walls of your container.
To do this, imagine a two-chamber container, with outer walls infinitely strong, but with a piston in between them which is maintained at its central position by some force that ... | https://physics.stackexchange.com |
88,737 | [
"https://physics.stackexchange.com/questions/88737",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/32319/"
] | I'm talking about the maximum speed if let's say I have a car with the power $P = 1000 \text{W}$ and a force of friction of $5 \mbox{N}$ acting in the opposite direction. After some googling I found that the maximum speed is given by $P=Fv$, where $P$ is the power, $F$ is the force, and $v$ is the velocity.
I understa... | "Total energy of the Earth" is somewhat of an odd concept, but there's no reason we can't really entertain it. It brings up some genuinely difficult questions. The right way to approach this is to define the system correctly and then identify forms of energy content and flows.
Things to "count" in the Earth's energy... | The heat generated from the Earth's core is about 4x10^13 W while the Sun provides about 1.7x10^17W so although the Earth's core is slowly cooling this has very little effect on the Earth's temperature.
The Earth is in equilibrium between the energy received from the sun and the energy it emits into space. If the amou... | https://physics.stackexchange.com |
178,745 | [
"https://electronics.stackexchange.com/questions/178745",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/20210/"
] | I have a microcontroller with an active low reset pin. This pin is connected to a timer that periodically triggers a low edge and resets the microcontroller.
What would be the best circuit that would allow me to also manually trigger the reset pin through an external circuit while the pin is connected to the timer? Sh... | When either the timer output or the GPIO goes low, \$ \overline{\text{INT}}\$ goes low, so the gate is a positive true AND, 1/4 of an HC08 or somesuch.
<img src="https://i.stack.imgur.com/YVcZ9.png" alt="enter image description here">
or, better yet,
<img src="https://i.stack.imgur.com/XgYTU.png" alt="enter image de... | I assume your timer output is a push-pull circuit?
If you can configure it to be open-drain, then you just need a pull-up resistor on the reset line, and use a switch to short the reset input to ground.
If you can't configure the Timer output to be open-drain, then you just need a series resistor between the timer ... | https://electronics.stackexchange.com |
31,697 | [
"https://dsp.stackexchange.com/questions/31697",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/22597/"
] | Out of curiosity, is it possible to actually reverse a filtering on MATLAB. For example, if I have
<pre><code>[b,a] = butter(6,0.6);
dataIn = randn(1000,1);
dataOut = filter(b,a,dataIn);
</code></pre>
Is there some way to go from <code>dataOut</code> and obtain <code>dataIn</code> in this example? I was able to more... | In general it's only possible to implement causal and stable filters. There are exceptions where <em>marginally</em> stable filters are used, but this doesn't apply here. So if you want to invert a given filter, this is only possible if its zeros are inside the unit circle of the complex plane (such filters are called ... | I think the general approach is correct. You don't get the same result due to numerical instability of high order IIR filters. You may try breaking filter into cascade of 2 order filters and do the same afterwards (swapping a & b)
| https://dsp.stackexchange.com |
131,306 | [
"https://electronics.stackexchange.com/questions/131306",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/31389/"
] | Unfortunately I found the headers on my computer's belkin 3-port Firewire 800 all tilted back somehow, and they snapped off when I tilted them forward to where they should be. As a quick fix, I have a smaller Firewire 800 card, but, it is not fitting for several reasons.
As a result, I may be forced to cannibalize the... | Disclaimer: The answers I am about to give you are personal opinion based on my own experience. Do keep in mind though, that I own a full range of Wellers from small to large and some hot-air tools.
<ol>
<li>A: Should you just use the connectors from the smaller card? Only, and I do mean <em>only</em> if you are 100% ... | It's a little hard to tell from the picture, but the first thing to check for is whether any pads have lifted. If you got lucky, and they didn't, the next step is to clean the pads up - you'll need some flux, a desoldering braid and a regular soldering iron to do that. Finally, it looks unlikely that you'll be able to ... | https://electronics.stackexchange.com |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.